A prime mover, such as an internal combustion engine or the like, can be connected to a high speed, low torque hydrostatic transmission that may be directly mounted to a mechanical speed reduction device, such as a gearbox. A hydrostatic transmission is particularly suitable to provide traction drive for a light vehicle, such as turf machines, lawn tractors, ride-on lawn mowers, and like devices. A hydrostatic transmission may be connected to a variety of gearboxes and transaxles, so the same components can be utilized on a wide variety of light vehicle models. A simple usage of hydrostatic transmissions is on zero-turn radius vehicles, including zero-turn radius mowers and tractors.
Generally, a hydrostatic transmission includes a hydraulic pump and a hydraulic motor. The hydraulic pump usually is a piston-type pump including a plurality of reciprocating pistons which are in fluid communication through hydraulic porting with the hydraulic motor. Rotation of the hydraulic pump against a moveable swash plate creates an axial motion of the pump pistons that forces hydraulic fluid through the hydraulic porting to the hydraulic motor to drive the motor, which allows the transmission output speed to be varied and controlled. The rotation of the hydraulic motor may be used to drive an output shaft, which in turn ultimately drives a wheel axle of a light vehicle of the types described above.
Because of the size constraints associated with light vehicles, it has been difficult to provide a combined hydrostatic transmission and gearbox assembly that is compact, cost effective, and easy to assemble. Current solutions for combining hydrostatic transmissions with gearboxes incorporate such components into an integrated housing rather than as modular components. As a result of such non-modular configurations, there is typically no ability to interchange the hydrostatic transmission with different configurations of gearbox components, which would be desirable to provide flexibility of usage with different types of light vehicle configurations.